Separation of hydrocarbon mixtures to recover aromatic hydrocarbons utilizing lactone-water solvents



Dec. 6, 1960 HYDROCARBONS UTILIZING LACTONE-WATER SOLVENTS D. MORIN SEPARATION OF HYDROCARBO ET N MIXTURES T0 RECOVER AROMATIC Filed 001;. 25, 1954 Solvent Feed oil Raffinate l0 storage storage l storage Water Raftinate 5 phase Extractlon 3 extraction 7 column column I V Aromatic hydrocarbon Condenser Extraction phase 'extraction column storage l3 Distlllation OWE! I6 INVENTOR. Richard D. Morin By John B. Flshel Arthur E. Bearse ATTQRNEYS.

2,963,429 SEPARATION OF 'HYDROCARBON MIXTURES T RECOVER AROMATIC HYDROCARBONS 'UTI LIZING LACTONE-WATER SOLVENTS Filed Oct. 25, 1954,- Ser. N0."464,518 9 Claims. 01. 208324) This invention relates to the separation of hydrocarbon mixtures. In particular, this invention is concerned with the separation of aromatic hydrocarbons from nonaromatic hydrocarbons. By aromatic hydrocarbons are meant those hydrocarbons which contain one or more benzene rings or related condensed aromatic rings such as naphthalene, phenanthrene, anthracene, acenaphthene, etc., and alkylated and alkenylated derivatives of these. Nonaromatic hydrocarbons include the acyclic and alicyclic, saturated and unsaturated hydrocarbons.

Separation of these two classes of hydrocarbons has become of increasing importance industrially, and many methods have been proposed for the separation of aromaticfrom nonaromatic hydrocarbons. The complex mixtures of hydrocarbons which occur naturally in petroleum, or those obtained from various refinery processing steps, often contain mixtures of aromatic and nonaro matic hydrocarbons which aredifiiculty separable from each other, if at all, by fractional distillation methods. Selective solvent extraction, selective adsorption'o'n solid adsorbents such as silica gel, and extractive distillation have been used with varying degrees of success. In the selective solvent method, a solvent must preferentially dissolve the aromatic hydrocarbons'to form a separable extract phase richer in aromatic hydrocarbons and a rafiinate poorer in aromatic hydrocarbons than the original hydrocarbon mixture. A' good selective solvent should show a high degree of selectivity for aromatic hydrocarbons, should have a low solubility in the rafiinate, should be readily separable froin'the aromatic hydrocarbons in the extract phase,- should be easily recoverable, and should be stable to allow recycling; Solvents which have been used for selective extraction'of aromatic hydrocarbons from mixtures with other hydrocarbons include sulfur dioxide,-furfural, diethylene glycol, polyethylene glycols, dimethyl formamide, oxyclipropionitrile, etc. These solvents are not entirely suitable in all respects because of either one or moredisadvantages due to poor selectivity, high solubility in the rafiinate, diificulties in recovery, or instability in subsequent recycling.

The object of this invention is the separation of aromatic hydrocarbons from nonaromatic hydrocarbons by means of a selective solvent. A further object is to provide a method for obtaining aromatic hydrocarbons substantially free from nonaromatic hydrocarbons by means of an efiective selective solvent. Still another object is to provide a cyclic process wherein the selective solvent can be easily recovered and reused in the vprocess.

The objects of this invention are accomplished by extraction of a mixture of aromatic and nonaromatic hydrocarbons with a solvent selected from the class of cyclic inner esters of gamma-hydroxyacids, commonly known as gamma-lactones. The gamma-lactones operable for the purposes of this invention are the lactones of the saturated and unsaturated gamma-hydroxy butanoic acids and the methyl-substituted lactones of these acids.

tes Patent 2,963,429 Patented Dec. 6, 1960 Specific examples representative of these gamma-lactones;

are gamma-butyrolactone,- gamma-methyl-gamma-butyrolactone (gamma-valerolactone) and gamma-butenolactone (gamma-crotonolactone).

In practice, the hydrocarbon mixture containing arcmatic and nonaromatic hydrocarbons is admixed thoroughly with the selective solvent selected from the aforementioned compounds byany suitable means, such as mechanical agitation or in a counter-current extraction column. Two immiscible phases are formed which are separated. The upper phase or rafiinate has an appreciably lower content of aromatic hydrocarbons than the original mixture and contains a small amount of selective solvent; The raflinate may be washed with water to remove the small amount of solvent dissolved therein.

The lower extract phase is composed of a solution of.

aromatic hydrocarbons in the selective solvent. By regulation of conditions such as temperature, ratio of selective solvent to the original hydrocarbon mixture, and Water content of the selective solvent, varying amounts of the aromatic hydrocarbons originally present can be removed. Thus, it is possible to obtain raffinates which are substantially free of aromatic hydrocarbons and extract phases which contain virtually all of the aromatic hydrocarbons of the original mixture. It is also possible to vary the'amount of the aromatic hydrocarbon in the extract phase by proper control of temperature, solventhydrocarbon ratio, and water content in the solvent.

Que of the outstanding features of the selective solvents of this invention is their case of removal from hydrocarbons by water washing. To recover the aromatic hydrocarbons, the extract phase is contacted with water. The selective solvent separates with the water as an aqueous solution immiscible with the aromatic hydrocarbon fraction. Phase separation may be facilitated by dilutionwith a low-density, hydrocarbon or mixture of hydrocarbons. The aromatic fraction, after distilling ofl the diluent, may, if desired, be further processed by distillation, but is suitable for many uses without further treatment. Recovery of the selective solvent from the aqueous phase solution is efiected by distillation which gives an aqueous'distillate and a residue of solvent. The recovered solventthen may be reused to treat more of the hydrocarbon mixture.

The solvents in the "class defined above are stable under the conditions of the extraction and recovery process, and have been recycled without evidence of deterioration. The only additional solvent needed is to make up any operating losses. In the solvent recovery step, it is not necessary to remove the last traces of water, since small amounts of Water up to ten percent by weight of the selective solvent can be tolerated. In certain cases, the presence of water in the:solvent is beneficial, since this gives increased selectivity, although the capacity of the solvent is somewhat reduced.

The drawing in Fig. 1 is a diagrammatic representation of a cyclic process using the selective solvents of the present invention in a continuous process for the separation of-hyd-rocarbon mixtures. The drawing is described with reference to gamma-buty-rolactone extraction of light catalytic cycle oil, a refinery product comprising aromatic hydrocarbons and nonaromatic hydrocarbons in the boiling range of 400 to 600 F. The butyr-olactone from storage tank 1 is admitted through line 2 to the top of countercurrent extraction column 3. Light catalytic cycle oil from storage tank 4 is fed through line 5 to the bottom of the column 3. The ratio of buty-rolactone to hydrocarbon mixture is maintained at the desired level by controlling the fiow rates of the two liquids. In extraction column 3 intimate contact of the buty-rolactone with the light catalytic cycle oil is attained and the rafiinate and extract phases are formed and separated. The raffinate rises to the top and passes through line 6 to the bottom of countercurrent extraction column 7. Water is admitted to the top of column 7 through line 8, and any butyrolactone carried over in the raffinate is removed as a dilute aqueous solution which leaves the bottom of column 7 through line 9. The washed raffinate passes through line It) to rafiinate storage tank 11. If desired, the washed ratrinate may be subjected to further extraction with the gamma-lactones. Also, all or portions of the washed raffinate may be fed back or recycled to the extraction column 3 to obtain further extraction of any aromatic hydrocarbons remaining in the rafiinate.

The extract phase from the bottom of column 3 passes through line 12 to the lower end of countercurrent extraction column 13 where it is contacted with water to separate the butyrolactone from the aromatic hydrocarbon fraction. The latter fraction passes from the top of column 13 through line 14 to the aromatic hydrocarbon storage tank 15. If desired, a relatively low-boiling low-density diluent, such as hexane or gasoline, may be introduced into column 13, along with the extract, to lower the density of the aromatic hydrocarbon fraction and permit easier separation from the aqueous butyrolactone phase. This diluent may subsequently be removed from the higher boiling aromatic hydrocarbons by fractional distillation.

The aqueous solution of butyrolactone obtained from the extract phase is fed from the bottom of column 13 through line 16 to the distillation tower 17. Aqueous butyrolactone from the bottom of column 7 is also fed to tower 17 through line 9. Distillation of the aqueous butyrolactone gives water as the overhead fraction which is condensed in condenser 18 and then used to wash the extract phase by passage through line 19 to the top of column 13; part of this distillate is used to wash the raffinate by passage through line 20 to the top of column 7. The high-boiling residue from the distillation of the aqueous butyrolactone is substantially pure butyrolactone suitable for reuse. The recovered butyrolactone is removed from the bottom of tower 17 and is returned through line 21 to the butyrolactone storage tank 1.

The separation of aromatic hydrocarbons from nonaromatic hydrocarbons by the selective solvents of this invention may be performed at temperatures from below room temperature to temperatures as high as about 130 C. As the temperature increases the phase separation becomes less discrete until at above about 130 C., the solubility of the solvent in hydrocarbon mixture is too high and immiscible phases are not obtained. The process is usually carried out at ambient room temperatures, although other temperatures may be used in processing certain materials in order to decrease viscosities and to facilitate phase disengagement.

The following examples illustrate the invention, but are not intended to limit it in any way.

Example I Twenty-five milliliters of gamma-butyrolactone was shaken thoroughly with 25 milliliters of a light catalytic cycle oil containing approximately 25 percent by weight of aromatic hydrocarbons, and the two immiscible liquid phases were allowed to separate. The lower extract phase was added to an equal volume of water and mixed thoroughly. On standing a short time, the mixture separated into a lower aqueous phase containing most of the butyrolactone and an upper water-insoluble phase containing the aromatic hydrocarbon and a minor amount of the butyrolactone. The latter phase was washed well with water and dried. It had a refractive index (11 of 1.5741 and amounted to 6 milliliters or 24 percent by volume of the original cycle oil, and represented substantially all of the aromatics originally present.

The raftinate was washed well with water and dried. It had a refractive index (22 of 1.4781.

4 Example II The gamma-butyrolactone used in this example contained 8.5 percent by weight of water.

Twenty-five milliliters of this solvent was added to 76 milliliters of a light catalytic cycle oil containing about 25 percent by weight of aromatic hydrocarbons, and the mixture was agitated. On standing a short time, two phases separated. The lower or extract phase was withdrawn and mixed with an equal volume of water. On standing, an upper phase separated which consisted of aromatic hydrocarbon and some dissolved butyrolactone. This layer was washed well with water and dried. It had a refractive index (11 of 1.5979 and measured 4.5 milliliters or nearly six percent by volume of the original cycle oil.

A second extraction of the raifinate from this experiment using 25 milliliters of the wet butyrolactone gave an additional amount of aromatic hydrocarbon oil (n =l.5962) measuring 5.0 milliliters or 6.5 percent by volume of the first raflinate. Together these two extractions gave 12.5 percent by volume of the original cycle oil as an aromatic hydrocarbon fraction, which corresponds to recovery of 57 percent by weight of aromatic fraction originally present.

Example III A mixture containing 75 percent by weight of white gasoline (n =1.4023) and 25 percent by weight of benzene (n =1.4972) was mixed thoroughly with 40 percent by volume of gamma-butyrolactone containing 5 percent by weight of water. The lower extract phase was separated and diluted with an equal volume of water. The aromatic oil which separated was Washed with water three times and dried. It had a refractive index (n of 1.4718 and contained 73 percent by weight of benzene. This corresponds to recovery of 28 percent by weight of the benzene in the original mixture.

Example IV Twenty-five milliliters of gamma-methyl-gamma butyrolactone (gamma-valerolactone) was shaken thoroughly with 25 milliliters of a light catalytic cycle oil containing approximately 25 percent by weight of aromatic hydrocarbon. Two immiscible liquid phases were allowed to separate. The lower extract phase was added to an equal volume of water and mixed thoroughly. On standing a short time, the mixture separated into a lower aqueous phase containing most of the gamma-lactone and an upper water-insoluble phase containing the aromatic hydrocarbon and a minor amount of the gammalactone. The latter phase was washed well with water and dried. It had a refractive index (11 of 1.5513 and amounted to 8 milliliters, or 32 percent by volume of the original cycle oil, and represented a product which had been substantially enriched in aromatic hydrocarbon content as compared to the original cycle oil.

Although the invention is particularly useful for the separation of aromatic hydrocarbons from light catalytic cycle oil, it is contemplated that the invention may be used in the extraction of other types of aromatic and nonaromatic hydrocarbon mixture. Obviously, there may be many modifications and variations of the extractive processes in the use of the invention.

What is claimed is:

1. The process of obtaining an extract rich in aromatic hydrocarbons from a mixture of aromatic and nonaromatic hydrocarbons by means of phase separation comprisng extracting said mixture with about 33 to 40% by volume of a selective solvent consisting essentially of at least one gamma-lactone selected from the group consisting of the lactones of the saturated and unsaturated gamma-hydroxy butanoic acids and the methylsubstituted lactones of said acids and five percent by weight of water, forming an extract phase comprising aromatic hydrocarbons dissolved in the major proportion of the solvent and a rafiinate phase comprising nonaromatic hydrocarbons, separating said extract phase from the rafiinate phase, washing said extract phase with water to form a water-gamma-lactone fraction immiscible with the aromatic hydrocarbons, and separating said fraction from the aromatic hydrocarbons.

2. The process of obtaining an extract rich in aromatic hydrocarbons from light catalytic cycle oil comprising extracting said oil with about 33 to 40% by volume of a selective solvent consisting essentially of at least one gamma-lactone selected from the group consistingof the lactones of the saturated and unsaturated gama-hydroxy butanoic acids and the methyl-substituted lactones of said acids and five percent by weight of water, forming an extract phase comprising aromatic hydrocarbons dissolved in the major proportion of the solvent and a raflinate phase comprising nonaromatic hydrocarbons, separating said extract phase from the rafiinate phase, washing said extract phase With water to form a water-gamma-lactone fraction immiscible with the aromatic hydrocarbons, and separating said fraction from the aromatic hydrocarbons.

3. In a process of obtaining an extract rich in aromatic hydrocarbons from a mixture of aromatic and nonaromatic hydrocarbons in which the mixture of aromatic and nonaromatic hydrocarbons are treated with about 33 to 40% by volume of a selective solvent comprising at least one gamma lactone selected from the group consisting of the lactones of the saturated and unsaturated gamma-hydroxy-butanoic acids and the methyl substituted lactones of said acids, the improvement which comprises introducing five percent by weight of water into the solvent prior to the treatment step.

4. The process of obtaining an extract rich in aromatic hydrocarbons from a mixture of aromatic and nonaromatic hydrocarbons by means of phase separation comprising extracting said mixture with about 33 to 40% by volume of a selective solvent comprising at least one gamma-lactone selected from the group consisting of the lactones of the saturated and unsaturated gamma-hydroxy butanoic acids and the methyl substituted lactones of said acids and five percent water to form an extract phase comprising aromatic hydrocarbons dissolved in the major portion of said solvent.

5. The process of obtaining an extract rich in aromatic hydrocarbons from light catalytic cycle oil comprising extracting said oil with from about 33 to 40% by volume of a selective solvent comprising at least one gamma-lactone selected from the group consisting of the lactones of the saturated and unsaturated gamma-hydroxy butanoic acids and the methyl substituted lactones of said acids and five percent by weight of water to form an extract phase comprising aromatic hydrocarbons dissolved in the major portion of the solvent.

6. In a cyclic process of separating aromatic hydrocarbons from a mixture of aromatic and nonaromatic hydrocarbons by means of phase separation comprising the steps of contacting the hydrocarbon mixture with from about 33 to 40% by volume of a selective solvent comprising at least one gamma-lactone selected from the group consisting of the lactones of the saturated and unsaturated gamma-hydroxy butanoic acids and the methyl substituted lactones of said acids and five percent of water by weight whereby an extract phase and a rafiinate is formed, separating said extract phase from said raffinate, washing said extract phase with water to form a water-gamma-lactone fraction immiscible with the aromatic hydrocarbons, separating said fraction from the immiscible aromatic hydrocarbons, separating the gamma-lactone from said fraction, and recycling said gamma-lactone and five percent Water for contact with additional hydrocarbon mixtures.

7. The cyclic process of separating aromatic hydrocarbons from a mixture of aromatic and nonaromatic hydrocarbons by means of phase separation comprising the steps of contacting said hydrocarbon mixture with from about 33 to 40% by volume of a selective solvent comprising at least one gamma-lactone selected from the group consisting of the lactones of the saturated and unsaturated gamma-hydroxy butanoic acids and the methyl substituted lactones of said acids and five percent by weight of water, whereby an extract phase and a rafiinate is formed, separating said extract phase from the rafiinate, washing said extract phase with water in the presence of a low-boiling, low-density hydrocarbon diluent tofacilitate the separation of a water-gamma-lactone fraction immiscible with the aromatic hydrocarbons, separating the gamma-lactone from said water-gamma-lactone frac tion, recycling said gamma-lactone with five percent by weight of water into contact with additional hydrocarbon mixtures, and recycling at least a portion of said raffinate into said hydrocarbon mixture.

8. The process of obtaining an extract rich in aromatic hydrocarbons from a mixture of aromatic and nonaromatic hydrocarbons by means of phase separation comprising extracting said mixture With from about 33 to 40% by volume of a selective solvent comprising gammabutyrolactone and five percent by weight of water to form an extract phase comprising aromatic hydrocarbon dissolved in the major portion of the solvent.

9. The process of obtaining an extract rich in aromatic hydrocarbons from a mixture of aromatic and nonaromatic hydrocarbons by means of phase separation comprising extracting said mixture with from about 33 to 40% by volume of a selective solvent comprising gammavalerolactone and five percent by weight of water to form an extract phase comprising aromatic hydrocarbons dissolved in the major portion of the solvent.

References Cited in the file of this patent UNITED STATES PATENTS 1,998,299 Pevere Apr. 16, 1935 2,148,710 Read Feb. 28, 1939 2,383,057 Gross et a1 Aug. 21, 1945 2,412,823 Mayland Dec. 17, 1946 2,503,200 Ham Apr. 4, 1950 2,507,861 Manley May 16, 1950 2,773,918 Stephens Dec. 11, 1956 2,831,905 Nelson Apr. 22, 1958 FOREIGN PATENTS 472,767 Great Britain Sept. 30, 1937 

5. THE PROCESS OF OBTAINING AN EXTRACT RICH IN AROMATIC HYDROCARBONS FROM LIGHT CATALYTIC CYCLE OIL COMPRISING EXTRACTING SAID WITH FROM ABOUT 33 TO 40% BY VOLUME OF A SELECTIVE SOLVENT COMPRISING AT LEAST ONE GAMMA-LACTONE SELECTED FROM THE GROUP CONSISTING OF THE LACTONES OF THE SATURATED AND UNSATURATED GAMMA-HYDROXY BUTANOIC ACIDS AND THE METHYL SUBSTITUTED LACTONES OF SAID ACIDS AND FIVE PERCENT BY WEIGHT OF WATER TO FORM AN EXTRACT PHASE COMPRISING AROMATIC HYDROCARBONS DISSOLVED IN THE MAJOR PORTION OF THE SOLVENT. 